Hologram recording medium, hologram recording device and method

ABSTRACT

A hologram recording medium ( 1 ) comprising a hologram recording layer ( 3 ) consisting of a photopolymer layer and formed on a substrate ( 2 ) consisting of a colorless, transparent resin film or the like, and a protection layer ( 4 ) consisting of a colorless, transparent resin film or the like and formed on the hologram recording layer ( 3 ), wherein the substrate ( 2 ) and the protection layer ( 4 ) are formed of a low-double-refraction material, and an optical axis of double refraction in the case of a strip-form medium is set to agree with a longer-side direction or a shorter-side direction thereof.

TECHNICAL FIELD

[0001] The present invention relates to a recording medium for hologram,and more particularly to a recording medium for hologram of the type inwhich hologram recording layer comprised of photo-polymer layer isconfigured to be put between protective layer and base. Further, thepresent invention relates to a hologram recording apparatus and ahologram recording method for recording hologram onto a recording mediumfor hologram.

BACKGROUND ART

[0002] Holographic stereogram is prepared, e.g., by recording, insuccession, onto single recording medium for hologram as strip-shaped ordot-shaped element hologram, a large number of pictures, as originalpicture, which are obtained by successively photographing object fromdifferent points of observation.

[0003] For example, in preparing holographic stereogram having parallaxinformation only in the lateral direction, such an approach is employedas shown in FIG. 1 to first photograph in succession object 100 fromdifferent points of observation in the lateral direction to therebyobtain parallax picture train 101 consisting of plural pictures havingparallax information in the lateral direction. It is to be noted that itis sufficient that such parallax picture train 101 is not pictureobtained by actually photographing object, but may be, e.g., CAD(Computer Aided Design) picture or CG (Computer Graphics) picturegenerated by computer etc. Further, respective pictures 102 constitutingthis parallax picture train 101 are recorded in succession onto arecording medium 103 for hologram as strip-shaped element hologram insuch a manner that they are successive in the lateral direction. Thus,holographic stereogram having parallax information in the lateraldirection can be obtained.

[0004] In this holographic stereogram, since information of pluralpictures 102 obtained by successively photographing object 100 fromdifferent points of observation in the lateral direction are recorded insuccession in such a manner that they are successive in the lateraldirection as strip-shaped element hologram, when observer looks at thisholographic stereogram by the both eyes, two-dimensional picture imagesrespectively imaged on his left and right eyes are different. Thus, theobserver feels parallax so that three-dimensional picture image isreproduced.

[0005] Meanwhile, element holograms of the above-mentioned holographicstereogram are recorded onto recording medium for hologram usingphotosensitive material as recording material in a manner stated below.Namely, in recording element holograms onto the recording medium forhologram, laser beams of good coherence are branched, and one branchedlaser beam is irradiated in a manner perpendicular to one surface of therecording medium for hologram as projected image (object light) whichhas been configured to undergo two-dimensional picture modulation bypicture display means, e.g., liquid crystal panel, etc. Further, theother branched laser beam is irradiated at a predetermined angle ontothe other surface of the recording medium for hologram as referencelight. Thus, interference patterns are formed as change of refractiveindex or transmission factor at the photosensitive material of therecording medium for hologram so that element holograms are recorded.

[0006] As recording medium for hologram, there may be used, e.g.,recording medium of the type in which hologram recording layerconsisting of photosensitive material such as photo-polymer, etc. isconfigured to be put between protective layer and base. The object lightand the reference light are irradiated in the state of linearpolarization from one surface and the other surface of the hologramrecording layer to form interference patterns to record elementholograms. It is to be noted that the photosensitive material of thehologram recording layer is not limited to photo-polymer, but there maybe used other photosensitive material, e.g., silver salt material orgelatin bichromate, etc.

[0007] As the protective layer and the base of such recording medium forhologram, the so-called optical material such as optically transparentresin or glass, etc. is used. Further, as such protective layer andbase, there is exemplified, e.g., transparent resin plate of such aspolycarbonate, polyolefin, PMMA (polymethyl methacrylate), etc. asdescribed in the Japanese Patent Publication No. H6-214117. Furthermore,there are exemplified PMMA (polymethyl methacrylate), polycarbonate,polyolefin, diethylene glycol bisallyl carbonate, polystyrene, hardpolyvinyl chloride, methylmethacrylate-styrene copolymer resin,styrene-acrylonitrile copolymer resin, and poly (4-methylpentene-1),etc., as described in the Japanese Patent Publication No. H10-119163.Further, Japanese Patent Publication No. 11-338336 discloses as examplessilicon compositions, etc. of condensation reactive type, additionreactive type, non-solvent type, ultraviolet hardening type and electronbeam hardening type, etc.

[0008] In addition, as structure of hologram recording medium includinghologram recording layer consisting of photo-polymer layer serving asphotosensitive material as described above, there are, as the structurealready announced, “Step hen A. Zager and Andrew M. Weber, “Displayholograms in Du Pont's Ommidex films”, Proc. of SPIE, Vol. 1461 (1991)pages 58-67 [DuPont]”, “T. J. Trout, W. J. Gambogi and S. H. Stevenson,“Photopolymer Materials for Color Holography”, Proc. SPIE, Vol. 2577(1995) pages 94-105”, “Sylvia H. Stevenson, “DuPont multicolorholographic recording films”, Proc. of SPIE, Vol. 3011 (1997)”, “MasamiKawabata, Akihiko Sato, Iwao Sumiyosi and Toshihiro kubota,“Photopolymer system and its application to a color hologram” AppliedOptics, Vol. 33, No. 11 (Apr. 10, 1994) pages 2152-2156”, etc.

[0009] However, in the above-mentioned hologram recording layer, thereis the possibility that contrast of interference pattern within thehologram recording layer may be lowered, or partial uniformess may bedegraded by double refraction which is the optical characteristic ofmaterial of the base or the protective layer.

[0010] As described above, object light and reference light are incidenton the hologram recording layer as linearly polarized light to forminterference patterns. However, when there is double refractioncharacteristic (birefringence) in the base or the protective layer,plane of polarization becomes oblique or changes into ellipticallypolarized light when such light is passed (transmitted) through the baseor the protective layer. For this reason, contrast of interferencepattern within the hologram recording layer is lowered.

[0011] As a method of solving such a phenomenon, there is mentioned amethod of reducing retardation which is one of index values of doublerefraction, i.e., reducing difference between refractive index in thedirection in parallel to the optical axis and refractive index in thedirection perpendicular to the optical axis as described in the JapanesePatent Publication No. H7-114329, for example.

[0012] However, optical materials having small difference betweenrefractive indexes of doble refraction are expensive.; Further,according as double refraction becomes smaller or lesser, materials arelimited, resulting in higher cost.

[0013] In addition, in development and fixing of photosensitive materialsuch as silver salt material, gelatin bichromate, photo-polymer, etc.used in the hologram recording layer, development process and fixingprocess are carried out by acid/alkali, ultraviolet ray/visibleray/infrared ray, heat of high temperature or combination thereof, etc.

[0014] Under such circumstances, optical materials used in theprotective layer and the base are also required to have variousresistances or tolerances, e.g., chemicals resisting property such asacid resistance or alkali resistance, etc., water proof property such asmoisture proof property or swelling proof property, etc., light proofproperty such as yellowing proof property, etc., weathering resistanceproperty such as heat resistance property or yellowing resistanceproperty, etc.

[0015] Accordingly, optical materials having less double refraction andprovided with the above-mentioned resistances are limited and aretherefore very expensive.

DISCLOSURE OF THE INVENTION

[0016] The present invention has been proposed in view of actualcircumstances and is directed to a recording-medium for hologram inwhich projected light of a picture image and reference light areirradiated onto a hologram recording layer to thereby record thehologram, wherein a base and a protective layer of the hologramrecording layer comprise with material having less double refraction.

[0017] Further, a hologram recording apparatus according to the presentinvention is directed to a hologram recording apparatus adapted forirradiating projected light of picture image and reference light onto ahologram recording layer to thereby record hologram, wherein axialdirection of double refraction of base and protective layer of thehologram recording layer is configured to be coincided with polarizationof the reference light and object light.

[0018] In addition, a hologram recording method according to the presentinvention is directed to a hologram recording method for irradiatingprojected light and reference light of a picture image onto a hologramrecording layer to thereby record hologram, wherein axial direction ofdouble refraction of a base and a protective layer of the hologramrecording layer coincides with polarized light of the reference lightand object light.

[0019] Still further objects of the present invention and more practicalmerits obtained by the present invention will become more apparent fromthe description of the embodiments which will be given below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a view for explaining procedure-for making holographicstereogram.

[0021]FIG. 2 is a view for explaining photosensitive process ofphoto-polymerization type photo-polymer.

[0022]FIG. 3A is a view for explaining initial state in thephotosensitive process of photo-polymerization type photo-polymer.

[0023]FIG. 3B is a view for explaining exposure state in thephotosensitive process of photo-polymerization type photo-polymer.

[0024]FIG. 3C is a view for explaining fixing state in thephotosensitive process of photo-polymerization type photo-polymer.

[0025]FIG. 4 is a view for explaining the state where one laser beam isincident on recording medium for hologram composed of base and hologrammrecording layer through polarization plate.

[0026]FIG. 5 is a view for explaining the state where reference lightand object light are respectively incident on recording medium forhologram composed of base, hologram recording layer and protective layerthrough polarization plates.

[0027]FIG. 6A is a view for explaining optical state of materials ofbase and protective layer constituting recording medium for hologram byusing refractive index elliptical body, wherein axial direction ofdouble refraction is configured to be coincided with thickness directionof the recording medium for hologram.

[0028]FIG. 6B is a view for explaining optical state of materials ofbase and protective layer constituting recording medium for hologram byusing refractive index elliptical body, wherein axial direction ofdouble refraction is configured to be coincided with a direction of thelonger side of the recording medium for hologram.

[0029]FIG. 6C is a view for explaining optical state of materials-ofbase and protective layer constituting recording medium for hologram byusing refractive index elliptical body, wherein axial direction ofdouble refraction is configured to be coincided with a direction of theshorter side of the recording medium for hologram.

[0030]FIG. 7 is a view showing the configuration of a holographicsteteogram preparing apparatus.

[0031]FIG. 8A is a view for explaining the configuration of exposureprocessing unit in the above-mentioned holographic stereogram preparingapparatus, wherein the entire optical system is viewed from the upwarddirection.

[0032]FIG. 8B is a view for explaining the configuration of exposureprocessing unit in the above-mentioned holographic stereogram preparingapparatus, wherein the portion for object light of the optical system isviewed from lateral direction.

[0033]FIG. 9 is a view for explaining detailed configuration of printerhead portion in the above-mentioned holographic stereogram preparingapparatus.

[0034]FIGS. 10A and 10B are views for explaining states of doublerefraction in the case where laser beams are obliquely incident and inthe case where laser beams are perpendicularly incident.

[0035]FIG. 11 is a cross sectional view of recording medium for hologramof five layer structure comprising two hologram recording layers.

[0036]FIG. 12 is a cross sectional view of recording medium for hologramof seven layer structure comprising three hologram recording layers.

BEST-MODE FOR CARRYING OUT THE INVENTION

[0037] Preferred embodiments of the present invention will now bedescribed with reference to the attached drawings. It should be notedthat the present invention is not limited to the following examples, andit is therefore needless to say that modification/change may be madewithin the range which does not depart from the gist of the presentinvention.

[0038] Initially, explanation will be given with reference to FIG. 2 inconnection with a more practical example of a recording medium forhologram. This recording medium 1 for hologram is adapted so that ahologram recording layer 3 comprised of photo-polymer layer is formed ona base 2 comprised of colorless and transparent resin film, etc. and aprotective layer 4 comprised of colorless and transparent resin film,etc. is formed on the hologram recording layer 3. Thicknesses of thebase 2 and the protective layer 4 and intermediate layer which will bedescribed later are 5 μm to 100 μm, and thickness of the hologramrecording layer 3 is 20 μm.

[0039] It is preferable that there is used for the hologram recordinglayer 3 photo-polymer configured to be of film structure, which issuitable for recording interference patterns taking place byinterference between reference light and object light as change ofrefractive index. In the photo-polymer configured to be of filmstructure, by irradiating light, refractive index of material ischanged. In this embodiment, as the hologram recording layer 3, there isused, e.g., photopolymerization type photo-polymer such as “OMNI-DEX”(Trade Name) by DuPont Company, etc. In the photopolymerization typephoto-polymer, in the initial state, as shown in FIG. 3A, monomers Mareuniformly dispersed within matrix polymer. Oh the contrary, when lightLa of power of about 10 to 400 mJ/cm² is irradiated as shown in FIG. 3B,monomers M of the exposed portions are polymerized in dependency uponpower of irradiated light La. As a result, densities of monomers locallychange so that refractive index modulation takes place. Thereafter, byirradiating ultraviolet rays Lb of power of about 1000 mJ/cm² onto theentire surface as shown in FIG. 3C, polymerization of monomers M iscompleted. Thus, refractive index modulation degree is enhanced and therefractive index modulation is fixed.

[0040] Meanwhile, in recording three-dimensional picture onto hologramrecording layer 3 comprised of the above-mentioned photo-polymerizationtype photo-polymer, as described later, reference light is transmittedthrough the base 2 so that it is incident on the hologram recordinglayer 3, and object light is transmitted through the protective layer 4so that it is incident on the hologram recording layer 3. Thus, suchinterference patterns are recorded onto the hologram recording layer 3.Accordingly, the base 2 and the protective layer 4 are required to haveoptical characteristics such as less double refraction, less lightscattering and high light transmission factor, etc. Particularly, sincewhen rays of linearly polarized light of object light and referencelight are transmitted through the base 2 and the protective layer 4,plane of polarization becomes oblique or they change into rays ofelliptical polarized light different from each other in dependency upondouble refraction of the base 2 and the protective layer 4, there is thepossibility that contrast of interference pattern within the hologramrecording layer 3 may be lowered.

[0041] How double refraction of the base 2 or double refraction of theprotective layer 4 affects contrast of interference pattern formed atthe hologram recording layer 3 will be described below in detail.

[0042] First, how polarization state changes in the case where laserbeams having linearly polarized light are incident on the hologramrecording layer through the base or the protective layer having doublerefraction will be explained.

[0043] The state where one laser beam L is incident, through apolarization plate 50, on a recording medium 51 for hologram composed ofa hologram recording layer 53 provided at one side and a base 52provided at the other side as shown in FIG. 4 is assumed as simplemodel.

[0044] Laser beam L is incident on the recording medium 51 for hologramthrough the polarization plate 50 and is transmitted through the base 52having double refraction so that there takes place change in thepolarization state. Thereafter, such laser beam is incident on thehologram recording layer 53. It is here to be noted that while laserbeam L is assumed to be incident on the recording medium 51 for hologramthrough the polarization plate 50, such explanation is given for thepurpose of facilitating that laser beam L is linearly polarized in thex-direction, and it is assumed that there is no absorption by thepolarization plate 50.

[0045] Here, it is assumed-that wavelength of laser beams is λ, electricfield vector of laserbeams in the state linearly polarized in thex-direction is {overscore (E)}^(in), and thickness of base-having doublerefraction is d. Here, for the brevity, the optical axis of the basehaving double refraction is assumed to be within the xy plane,refractive index in the axial direction is assumed to be n_(e),refractive index in-the direction perpendicular thereto is assumed to ben_(o), and direction of the axis is assumed to form angle φ in thex-direction.

[0046] Further, unit vectors in x, y and z directions are respectivelyassumed to be {overscore (e)}_(x), {overscore (e)}_(y), {overscore(e)}_(z), and unit vectors in the axis direction of double refractionand in the direction perpendicular thereto are respectively assumed tobe {overscore (e)}_(e), {overscore (e)}_(o). At this time, with respectto these unit vectors, the relationship indicated by the followingformula (1) holds. $\begin{matrix}\left\{ {\begin{matrix}{{\overset{\_}{e}}_{e} = {{\cos \quad {\varphi \cdot {\overset{\_}{e}}_{x}}} + {\sin \quad {\varphi \quad \cdot {\overset{\_}{e}}_{y}}}}} \\{{\overset{\_}{e}}_{o} = {{\sin \quad {\varphi \cdot {\overset{\_}{e}}_{x}}} - {\cos \quad {\varphi \cdot {\overset{\_}{e}}_{y}}}}}\end{matrix}\left\{ \begin{matrix}{{\overset{\_}{e}}_{x} = {{\cos \quad {\varphi \cdot {\overset{\_}{e}}_{e}}} + {\sin \quad {\varphi \quad \cdot {\overset{\_}{e}}_{o}}}}} \\{{\overset{\_}{e}}_{y} = {{\sin \quad {\varphi \cdot {\overset{\_}{e}}_{e}}} - {\cos \quad {\varphi \cdot {\overset{\_}{e}}_{o}}}}}\end{matrix} \right.} \right. & (1)\end{matrix}$

[0047] In this model, the electric field-vector of the incident laserbeams L is expressed as E^(in)=E^(in) e_(x) by using complex amplitudeE^(in) and laser beams L in the state linearly polarized in thex-direction is assumed to be incident on the base 52 having doublerefraction. When electric field vector before laser beams are-incidentis separated into two components {overscore (E)}_(e) ^(in), {overscore(E)}_(i) ^(in) the direction of the axis of double refraction and in thedirection perpendicular thereto, it is expressed as the followingformula (2) $\begin{matrix}{{\overset{\_}{E} = {{{\overset{\_}{E}}_{e}^{in} + {\overset{\_}{E}}_{o}^{in}} = {{E^{in}{\overset{\_}{e}}_{x}} = {{E^{in}\cos \quad {\varphi \cdot {\overset{\_}{e}}_{e}}} + {E^{in}\sin \quad {\varphi \quad \cdot {\overset{\_}{e}}_{o}}}}}}}\left\{ \begin{matrix}{{\overset{\_}{E}}_{e}^{in} = {{E^{in}\cos^{2}\quad {\varphi \cdot {\overset{\_}{e}}_{x}}} + {E^{in}\cos \quad \varphi \quad \sin \quad {\varphi \cdot {\overset{\_}{e}}_{y}}}}} \\{{\overset{\_}{E}}_{o}^{in} = {{E^{in}\sin^{2}\quad {\varphi \cdot {\overset{\_}{e}}_{x}}} - {E^{in}\sin \quad \varphi \quad \cos \quad {\varphi \quad \cdot {\overset{\_}{e}}_{y}}}}}\end{matrix} \right.} & (2)\end{matrix}$

[0048] These electric field vectors of two components are passed throughthe base 52 having double refraction, thereby they respectively undergophase changes of 2πin_(e)d/λ and 2πin_(o)/λ. Thus, electric field vector{overscore (E)}^(out) out passed/emitted through the base 52 andincident on the hologram recording layer 53 is expressed as thefollowing formulas (3), (4) in the state separated into two components{overscore (E)}_(e) ^(out), {overscore (E)}_(o) ^(out) in the directionof the axis and in the direction perpendicular thereto. $\begin{matrix}\begin{matrix}{{\overset{\_}{E}}_{e}^{out} = {{\overset{\_}{E}}_{e}^{in} \cdot {\exp \left( {2\pi \quad i\quad n_{e}{d/\lambda}} \right)}}} \\{= {{{\overset{\_}{E}}^{in}\cos^{2}{\varphi \cdot {\exp \left( {2\quad \pi \quad i\quad n_{e}{d/\lambda}} \right)} \cdot {\overset{\_}{e}}_{x}}} + {{\overset{\_}{E}}^{in}\cos \quad \varphi \quad \sin \quad {\varphi \cdot {\exp \left( {2\quad \pi \quad i\quad n_{e}{d/\lambda}} \right)} \cdot {\overset{\_}{e}}_{y}}}}}\end{matrix} & (3) \\\begin{matrix}{{\overset{\_}{E}}^{out} = {{\overset{\_}{E}}_{o}^{in} \cdot {\exp \left( {2\pi \quad i\quad n_{o}{d/\lambda}} \right)}}} \\{= {{E^{in}\sin^{2}{\varphi \cdot {\exp \left( {2\quad \pi \quad i\quad n_{o}{d/\lambda}} \right)} \cdot {\overset{\_}{e}}_{x}}} - {E^{in}\sin \quad \varphi \quad \cos \quad {\varphi \cdot {\exp \left( {2\quad \pi \quad i\quad n_{o}{d/\lambda}} \right)} \cdot {\overset{\_}{e}}_{y}}}}}\end{matrix} & (4)\end{matrix}$

[0049] Thus, electric field vector E^(out) is expressed as the followingformula (5). $\begin{matrix}\begin{matrix}{{\overset{\_}{E}}^{out} = {{\overset{\_}{E}}_{e}^{out} + {\overset{\_}{E}}_{o}^{out}}} \\{= {E^{in}{\left\{ {{\cos^{2} \cdot \varphi \cdot {\exp \left( {2\quad \pi \quad i\quad n_{e}{d/\lambda}} \right)}} + {\sin^{2}{\varphi \cdot {\exp \left( {2\quad \pi \quad i\quad n_{o}{d/\lambda}} \right)}}}} \right\} \cdot}}} \\{{~~}{{\overset{\_}{e}}_{x} + \quad {E^{in}\cos \quad \varphi \quad \sin \quad {\varphi \cdot \left\{ {{\exp \left( {2\quad \pi \quad i\quad n_{e}{d/\lambda}} \right)} - {\exp \left( {2\quad \pi \quad i\quad n_{o}{d/\lambda}} \right)}} \right\} \cdot {\overset{\_}{e}}_{y}}}}}\end{matrix} & (5)\end{matrix}$

[0050] From this formula, it is seen that when φ=0[rad], φ=π/2[rad] orn_(e)=n_(o) does not hold by the effect of double refraction, the e_(y)component takes place in electric field vector E_(out) incident on thehologram recording layer 53, thus the changes of polarization statetaking place, which change is, for example, the rotation of plane ofpolarization with respect to incident light, etc.

[0051] It is to be noted that it has been explained for simplificationthat optical axis of base having double refraction is within the xyplane. However, similar explanation can be given to the case where theoptical axis of the base having double refraction is not within the xyplane while replacing two refractive indexes n₁, n₂ which form long axisand short axis of ellipse indicating refractive index by n_(e), no, inview of the relationship between propagation direction of rays (pointingvector) and refractive index vector plane, i.e., in view of therelationship indicated by ellipse prepared by plane perpendicular towave vector and refractive index, elliptical body from an intuitivepoint of view.

[0052] Secondly, an explanation will be given-in connection with thecase where, for recording of hologram, two laser light fluxes havinglinear polarization are passed through the base or the protective layerhaving double refraction so that they are incident on the hologramrecording layer and-interfere with each other.

[0053] There is assumed two light flux interference model that, as shownin FIG. 5, reference light L4 is transmitted through the base 2 and isincident on the hologram recording layer 3 with respect to the recordingmedium 1 for hologram composed of base 2, hologram recording layer 3 andprotective layer 4, and object light L3 is transmitted through theprotective layer 4 and is incident on the hologram recording layer 3,whereby interference patterns thereof are formed on the hologramrecording layer 3.

[0054] Reference light LA is incident on the recording medium 1 forhologram through a polarization plate 60, and is transmitted through thebase 2 having double refraction so that there takes place change in thepolarization state. Thereafter, this reference light LA is incident onthe hologram recording layer 3. On the other hand, object light L3 isalso incident on the-recording medium 1 for hologram through apolarization plate 61, and is transmitted through the protective layer 4having double refraction so that there takes place change in thepolarization state. Thereafter, this object light is incident on thehologram recording layer 3. It is to be noted that reference light LAand object light L3, are assumed to be incident on the recording medium1 for hologram through polarization plates 60, 61, such assumption ismade in order to easily understand that laser beams are linearlypolarized in the x-direction and it is assumed that there is noabsorption by the polarization plate.

[0055] Here, wavelength of laser beams of reference light L4 and objectlight.L3 is assumed to be λ. With respect to the reference light LAside, electric field vector of reference light in the state linearlypolarized in the x-direction is assumed to be E^(ref,in) and thicknessof base 2 having double refraction is assumed to be d^(ref). It is hereto be noted for simplification that optical axis of base 2 having doublerefraction is assumed to be within the xy plane, refractive index in theaxial direction is assumed to be n_(e) ^(ref), refractive index in thedirection perpendicular thereto is assumed to be n_(o) ^(ref), anddirection of the axis is assumed to form angle φ in the x-direction.With respect to the object light L3 side, electric field vector ofobject light L3 in the state linearly polarized in the x-direction isassumed to be {overscore (E)}^(obj,in) and thickness of the protectivelayer 4 having double refraction is assumed to be d^(obj). Here, forsimplification, the optical axis of the protective layer 4 having doublerefraction is assumed to be within xy-plane, refractive index in theaxial direction is assumed to be n_(e) ^(obj), refractive index inthe-direction perpendicular thereto is assumed to be n_(o) ^(obj))j anddirection of the axis is assumed to form angle Ψ in the x-direction.

[0056] In this model, electric field vector of incident reference light14 is assumed to be expressed as {overscore (E)}^(ref,in)=E^(ref,in){overscore (e)}_(x) by using complex amplitude E^(ref,in), and referencelight in the state linearly polarized in the x-direction is assumed tobe incident on the base 2 having double refraction. In addition,electric field vector of incident object light L3 is assumed to beexpressed as {overscore (E)}^(obi,in) E=E^(obj,in) in e by using,complex amplitude E^(obj,in) and object light L3 in the state linearlypolarized in the x-direction is assumed to be incident on the protectivelayer 4 having double refraction.

[0057] From the result obtained by the model shown in FIG. 4, electricfield vector {overscore (E)}^(ref,out) of reference L4 passed/emittedthrough the base 2 and incident on the hologram recording layer 3 isrepresented by the following formula (6). $\begin{matrix}\begin{matrix}{{\overset{\_}{E}}^{{ref},{out}} = {{\overset{\_}{E}}^{{ref},{out}} + {\overset{\_}{E}}_{o}^{{ref},{out}}}} \\{= {E^{{ref},{in}}\left\{ {{\cos^{2}{\varphi \cdot {\exp \left( {2\quad \pi \quad i\quad n_{o}^{ref}{d^{ref}/\lambda}} \right)}}} +} \right.}} \\{{{\left. {\sin^{2}{\varphi \cdot {\exp \left( {2\quad \pi \quad i\quad n_{o}^{ref}{d^{ref}/\lambda}} \right)}}} \right\}} \cdot {\overset{\_}{e}}_{x}} +} \\{{E^{{ref},{i\quad n}}\cos \quad \varphi \quad \sin \quad {\varphi \cdot \left\{ {{\exp \left( {2\quad \pi \quad i\quad n_{e}^{ref}{d^{ref}/\lambda}} \right)} -} \right.}}} \\{{\left. {\exp \left( {2\pi \quad i\quad n_{o}^{ref}{d^{ref}/\lambda}} \right)} \right\}} \cdot {\overset{\_}{e}}_{y}}\end{matrix} & (6)\end{matrix}$

[0058] Moreover, the electric field vector {overscore (E)}^(obj,out) ofthe object light L3 passed/emitted through the protective layer 4 andincident on the hologram recording layer 3 is represented by thefollowing formula (7). $\begin{matrix}\begin{matrix}{{\overset{\_}{E}}^{{obj},{out}} = {{\overset{\_}{E}}_{e}^{{obj},{out}} + {\overset{\_}{E}}_{o}^{{obj},{out}}}} \\{= {E^{{obj},\quad {i\quad n}}\left\{ {{\cos^{2}{\varphi \cdot {\exp \left( {2\quad \pi \quad i\quad n_{e}^{obj}{d^{obj}/\lambda}} \right)}}} +} \right.}} \\{{{\left. {\sin^{2}{\varphi \cdot {\exp \left( {2\quad \pi \quad i\quad n_{o}^{obj}{d^{obj}/\lambda}} \right)}}} \right\}} \cdot {\overset{\_}{e}}_{x}} +} \\{{E^{{obj},{i\quad n}}\cos \quad \varphi \quad \sin \quad {\varphi \cdot \left\{ {{\exp \left( {2\quad \pi \quad i\quad n_{e}^{obj}{d^{obj}/\lambda}} \right)} -} \right.}}} \\{{\left. {\exp \left( {2\pi \quad i\quad n_{o}^{obj}{d^{obj}/\lambda}} \right)} \right\}} \cdot {\overset{\_}{e}}_{y}}\end{matrix} & (7)\end{matrix}$

[0059] As a result, the light intensity I of interference patterns whichcan be formed on the hologram recording layer 3 is a square of absolutevalue of sum of the electric field vectors of the reference light L4 andthe object light L3, and is represented by the following formula (8)when phase change values taking place as the result of the fact thatrays of such light are passed through the base 2 and the protectivelayer 4 having double refraction are respectively indicated by N_(e)^(ref), N_(o) ^(ref), N_(e) ^(obj), N_(o) ^(obj). $\begin{matrix}\begin{matrix}{I = {{{\overset{\_}{E}}^{{ref},{out}} + {\overset{\_}{E}}^{{obj},{out}}}}^{2}} \\{= \left| \left\lbrack {{E^{{ref},\quad {i\quad n}}\left\{ {{\cos^{2}{\varphi \cdot N_{e}^{ref}}} + {\sin^{2}{\varphi \cdot N_{o}^{ref}}}} \right\}} + {{\overset{\_}{E}}^{{obj},{i\quad n}}\left\{ {{\cos^{2}{\varphi \cdot N_{e}^{obj}}} +} \right.}} \right. \right.} \\{{\left. {\left. {\sin^{2}{\varphi \cdot N_{o}^{obj}}} \right\}} \right\rbrack \cdot {\overset{\_}{e}}_{x}} +} \\{\left\lbrack {{E^{{ref},\quad {i\quad n}}\cos \quad {\varphi \cdot \sin}\quad {\varphi \cdot \left\{ {N_{e}^{ref} - N_{o}^{ref}} \right\}}} + {{\overset{\_}{E}}^{{obj},\quad {i\quad n}}\cos \quad \varphi \quad \sin \quad {\varphi \cdot}}} \right.} \\\left. {{\left. \left\{ {N_{e}^{obj} - N_{0}^{obj}} \right\} \right\rbrack} \cdot {\overset{\_}{e}}_{y}} \right|^{2} \\{= {{{E^{{ref},\quad {i\quad n}}\left\{ {{\cos^{2}{\varphi \cdot N_{e}^{ref}}} + {\sin^{2}{\varphi \cdot N_{o}^{ref}}}} \right\}} + {{\overset{\_}{E}}^{{obj},{i\quad n}}\left\{ {{\cos^{2}{\varphi \cdot N_{e}^{obj}}} +} \right.}}}} \\\left. {\left. {\sin^{2}\varphi \quad N_{o}^{obj}} \right\}} \middle| {}_{2} + \right. \\{\left| {{E^{{ref},\quad {i\quad n}}\cos \quad \varphi \quad \sin \quad {\varphi \cdot \left\{ {N_{e}^{ref} - N_{0}^{ref}} \right\}}} +} \right.} \\{\left. {E^{{obj},{i\quad n}}\cos \quad \varphi \quad \sin \quad \varphi \left\{ {N_{e}^{obj} - N_{o}^{obj}} \right\}} \right|^{2}}\end{matrix} & (8)\end{matrix}$

[0060] Here, the phase changes N_(e) ^(ref), N_(o) ^(ref), N_(e) ^(obj),N_(o) ^(obj) are represented by the following formula (9).

N _(e) ^(ref) =exp(2πin _(e) ^(ref) d ^(ref)/λ), N _(o) ^(ref) =exp(2πin_(o) ^(ref) d ^(ref)/λ) N _(o) ^(obj) =exp(2πin _(o) ^(obj) d ^(obj)/λ),N _(o) ^(obj) =exp(2πin _(o) ^(obj) d ^(obj)/λ)  (9)

[0061] From the formula of light intensity I of this interferencepattern, in the case where a certain reference light L4 and a certainobject light L3 which are respectively perpendicularly incident on therecording medium 1 for hologram are given, in order to maximize contrastof light intensity of interference pattern, polarization states ofreference light L4 and object light L3 are configured to be the same,i.e., relationship therebetween is configured to be represented by thefollowing formula (10).

|E ^(ref,in)cosφsinφ·{N _(e) ^(ref) −N _(o) ^(ref) }|=|E^(obj,in)cosφsinφ·{N _(e) ^(obj) −N _(o) ^(obj)}|  (10)

[0062] Here, for simplification, even in the case where lightintensities of reference light LA and object light L3 are equal to eachother (i.e., absolute values of complex amplitudes of the referencelight and the object light are equal to each other), namely,|E^(ref,in)|=|E^(obj,in)|1, it is necessary to satisfy the followingformula (11).

cosφsinφ·exp(2πin _(o) ^(ref) d ^(ref)/λ)−exp(2πin _(o) ^(ref) d^(ref)/λ)|=cosφsinφ·exp(2πin _(o) ^(obj) d ^(obj)/λ)−exp(2πin _(o)^(obj) d ^(obj)/λ)  (11)

[0063] As the result of the above, in order to satisfy this formula(11), such an approach is employed that, with respect to material of thebase 2, thickness is configured to be d^(ref), refractive index in theaxial direction of double refraction of the base is configured to ben_(e) ^(ref), refractive index in the direction perpendicular thereto isconfigured to be n_(o) ^(ref) and direction of the axis is configured toform angle φ in the x-direction, and, with respect to material of theprotective layer 4, thickness is configured to be d^(obj), refractiveindex in the axial direction of double refraction of the protectivelayer 4 is configured to be n_(e) ^(obj), refractive index in thedirection perpendicular thereto is configured to be n_(o) ^(obj), andaxial direction is configured to form angle Ψ in the x-direction. Thus,recording of hologram of good contrast of interference pattern which canbe formed at the hologram recording layer 3, i.e., high diffractionefficiency can be made.

[0064] As the solution of the above-mentioned formula (11), pluralsolutions are given by the above-mentioned eight values, i.e., d^(ref),n_(e) ^(ref), n_(o) ^(ref), φ, d^(obj), n_(e) ^(obj), n_(o) ^(obj), Ψ.Particularly, when (a) in the base, n_(e) ^(ref)=n_(o) ^(ref), φ=0[rad]or φ=π/2[rad] is configured to hold, (b) in the protective layer, n_(e)^(obj)=n_(o) ^(obj), Ψ=0[rad] or Ψ=π/2[rad] is configured to hold,satisfying of (a) and (b) at the same time constitutes one of solutions.

[0065] To put it in physical expression, satisfying of both phrases of(a), in the base, “there is no double refraction in the base” withrespect to incident direction of reference light, “direction of linearpolarization of reference light is the same as axial direction of doublerefraction of base” or “direction of linear polarization of referencelight is the same as direction perpendicular to the axis of doublerefraction of the base”, and (b), in the protective layer, “there is nodouble refraction in the protective layer” with respect to incidentdirection of object light, “direction of linear polarization of objectlight is the same as axial direction of double refraction of theprotective layer”, or “direction of linear polarization of object lightis the same as direction perpendicular to the axis of double refractionof the protective layer” constitutes one of solutions.

[0066] The relationship between these (a) and (b) results in therelationship between irradiation states of reference light and objectlight and the recording medium for hologram, and relates to a makingmethod or a recording apparatus for holographic stereogram or hologram.

[0067] On the contrary, geometrical shape of the recording medium forhologram and axial direction of double refraction of the base and theprotective layer constituting the recording medium for hologram areconfigured to have relationship similar to (a) and (b), thereby makingit possible to unify, every apparatuses, polarization states ofrecording apparatuses for holographic stereogram or hologram.

[0068] Namely, with respect to geometrical shape of the strip-shaped orthe like recording medium for hologram having the longer side and theshorter side, axial direction of double refraction of optical materialconstituting the recording medium for hologram is configured to becoincided with the longer side or the shorter side, or the directionperpendicular to the axis of double refraction is configured to becoincided with the longer side or the shorter-side.

[0069] When optical state of material of base 2 and protective layer 4constituting such a recording medium 1 for hologram is illustrated byusing refractive index elliptical body, there results optical state asshown in FIG. 6. This FIG. 6 shows the example where uniaxial opticalmaterial is used.

[0070] In FIG. 6A, axial direction Y of doble refraction of uniaxialoptical material is configured to be coincided with thickness directionof a strip-shaped recording medium 65 for hologram. By doing so, thereresults the state where there is no double refraction with respect tolaser beams L incident in a manner perpendicular to recording medium 65for hologram.

[0071] In FIG. 6B, axial direction Y of double refraction of uniaxialoptical material is configured to be coincided with a direction of thelonger side of strip-shaped recording medium 66 for hologram. Thereby,it is easy that there results the state where direction of linearpolarization is configured to be the same as axial direction of doublerefraction or the state perpendicular thereto with respect to laserbeams L incident on recording medium 66 for hologram.

[0072] In FIG. 6C, the axial direction Y of double refraction ofuniaxial optical material is configured to be coincided with a directionof the shorter side of strip-shaped recording medium 67 for hologram.Thereby, it is easy that there results the state where direction oflinear polarization is configured to be the same as axial direction ofdouble refraction or the state perpendicular thereto with respect tolaser beams L incident on recording medium 67 for hologram.

[0073] By the above-described invention, it is possible to univocallydetermine polarization state of the hologram recording apparatus in amanner coincided with geometrical shape of the strip-shaped recordingmedium for hologram as in the above-mentioned example shown. On thecontrary, such an approach is employed to unify and standardizepolarization states of hologram recording apparatuses every apparatuses,thereby making it possible to unify and standardize geometrical shape ofthe recording medium for hologram. Thus, in both the hologram recordingapparatus and the recording medium for hologram, mass production can bemade and reduction in cost can be realized.

[0074] Namely, as the base 2 and the protective layer 4, there is usedmaterial in which axial direction of double refraction is configured tobe coincided with geometrical shape of the recording medium forhologram, and is desirably used material of less double refraction, andinterference patterns of three-dimensional image are recorded onto thehologram recording layer 3. Thus, recording of interference patterns ofgood contrast can be carried out. Furthermore, by irradiatingreproduction light onto those interference patterns, re production ofhigh diffraction efficiency can be made, and reproduction image is ofhigh quality. From this fact, it can be said that there holds apredetermined relationship with respect to quality of reproductionimage, diffraction efficiency and quantity and state of doublerefraction.

[0075] Let suppose the case where polymer material (resin material) isused in the state of film (thin film structure) as optical materialsused for the protective layer and the base.

[0076] Even in the case where raw material having less double refractionis used as optical material, there are instances where double refractiontakes place at the time of molding. Particularly, in the case wherematerial is configured to be of film structure for the purpose of usingit as the base, the protective layer or the intermediate layer of therecording medium for hologram, since expansion process is added for thepurpose of molding, double refraction is easy to take place. This isbecause shape of refractive index elliptical body mainly depends uponpolarization state of molecular ring in polymer material. Namely,optical axis of double refraction greatly depends upon polarizationfactor and bonding direction of molecule.

[0077] Thus, in the case of allowing polymer material to be of filmstructure, although depending upon components of raw material used,quantity of double refraction becomes greatly different depending uponits manufacturing method. In particular, in expanding process, which istypical manufacturing method for film, there are many instances wheremolecular ring is expanded in expanding direction and double refractionwhich was less in the row material is also increased depending uponexpanding state.

[0078] Thus, the recording medium for hologram is used in the statewhere axial direction of double refraction is configured to be coincidedwith geometrical shape thereof as in this embodiment, thereby making itpossible to use such inexpensive material typically manufactured asoptical film.

[0079] In addition to the above, it is more desirable to use materialhaving less double refraction as raw material. As material having lessdouble refraction, there can be used, e.g., material obtained byallowing transparent resin (optical plastic, optical polymer) developedas base material for optical disc to be of film structure. In thestructure of the above-described and already announced recording mediumfor hologram, polyethylene terephthalate (PET), and vinyl chloride (PVC)are used, but such materials are not suitable from viewpoints of doublerefraction and transparency. As the material, material called non-doublerefractive optical polymer is desirable.

[0080] When desirable materials are exemplified, there is polycarbonateresin (PC). As material having double refraction lesser than that, thereis methacrylic resin (acryl, PMMA). As material having double refractionlesser than methacrylic resin, there are “ZEONEX” (Trade Name, NipponZeon Co., Ltd.), “ARTON” (Trade Name, JSR Kabushiki Kaisha), “APEL”(Trade Name, Mitsui Kagaku Kabushiki Kaisha) and “Olefin MaleimideCopolymer (Tosoh Kabushiki Kaisha) which are classified into alicyclicolefin (amorphous polyolefin). As other material having less doublerefraction, there is “Optolez” (Trade Name, Product Names OZ-1000,OZ-1100, OZ-1310, OZ-1330, etc., Hitachi Kasei Kogyo Kabushiki Kaisha)which is classified into alicydlic acryl.

[0081] In addition to the above, it is further desirable to use materialsuch that double refraction is difficult to take place with respect toexpansion. As one method thereof, there is used material manufactured bymethod of random-copolymerizing monomer indicating inverse (plus orminus) double refraction characteristic with the above-mentionedpolymer. In particular, it is desirable to use, as the base, theprotective layer and the intermediate layer of the recording medium forhologram, film by material in which stilbene is 3% doped by weight inPMMA as indicated in “Iwata et al. Proceedings of Polymer Society,V61.45, No. 3 page 461 (1996)”.

[0082] Three-dimensional picture is recorded, as holographic stereogram,onto recording medium for hologram in which hologram recording layer 3is configured to be put between the above-described base 2, protectivelayer 4 and/or intermediate layer which will be described later, whichconsist of materials as described above.

[0083] Subsequently, holographic stereogram preparing apparatus forrecording three-dimensional picture onto the above-described recordingmedium 1 for hologram as holographic stereogram will be described. Whileexplanation will be given here in connection with the apparatus forrecording strip-shaped plural element holograms onto one recordingmedium 1 for hologram to thereby prepare holographic stereogramconfigured to have parallax information in the lateral direction and-inthe longitudinal direction, there may be also mentioned, e.g., anapparatus for recording dot-shaped element hologram onto one recordingmedium 1 for-hologram to thereby prepare L holographic stereogramconfigured to have parallax information in the lateral direction and inthe longitudinal direction.

[0084] This holographic stereogram preparing apparatus is directed to amaking apparatus for the so-called one step holographic stereogram, andis adapted to output, as holographic stereogram, recording medium 1itself where interference pattern between object light and referencelight are recorded.

[0085] As shown in FIG. 7, this holographic stereogram preparingapparatus (unit) is composed of a data processing unit 21 for carryingout processing of picture data to be recorded, a computer 22 for controlwhich carries out control of the-entirety of this system, and anexposure processing unit 23 including an optical system for makingholographic stereogram.

[0086] The data processing unit 21 reads thereinto parallax picturetrain D1 from parallax picture train imaging section or parallax picturetrain generation computer, etc. to implement predetermined pictureprocessing for holographic stereogram, e.g., view point conversionprocessing and/or keystone distortion correction processing, etc. to theparallax picture train D1 by a picture processing computer 24 to store(record) picture data D2 to which-predetermined processing has beenimplemented into a memory section 25 such as memory or hard disc, etc.

[0087] In this example, the parallax picture train imaging sectiondelivers, to the picture processing computer 24, as parallax picturetrain D1, e.g., picture image obtained by photographing object fromdifferent plural view points in lateral direction by simultaneousphotographing by multi-eye type camera or successive photographing bymovement type camera, etc.

[0088] Furthermore, the parallax picture train generation computerprepares parallax picture train D1 consisting of plural picture imagesincluding parallax information by making use of the technique such asCAD or CG, etc. to deliver this parallax picture train D1 to the pictureprocessing computer 24.

[0089] Furthermore, the data processing unit 21 reads out, in order,picture data every one picture from the memory section 25 when preparingholographic stereogram to send out this picture data D3 to the controlcomputer 22.

[0090] The control computer 22 controls the exposure processing unit 23to record, in succession, as strip-shaped element holograms, pictureimages based on picture data D3 delivered from the data processing unit21 onto the recording medium 1 for hologram set within the exposureprocessing unit 23.

[0091] At this time, the control computer 22 carries out control ofshutter, display section and printer head portion, etc provided at theexposure processing unit 23 as described later. Namely, the controlcomputer 22 sends out a control signal S1 to the shutter to controlopening/closing operations of the shutter, delivers picture data D4 tothe display section to allow the display section to display pictureimage based on the picture data D4, and sends out a control signal S2 tothe printer head portion to control sending operation, etc. of therecording medium 1 for hologram by the printer head portion.

[0092] Subsequently, the exposure processing unit 23 will be describedin detail with reference to the attached drawings. Here, FIG. 8A is aview in which the optical system of the entirety of the exposureprocessing unit 23 is viewed from the upper direction and FIG. 8B is aview in which the portion for object, light of the optical system of theexposure processing unit 23 is viewed from lateral direction. It is tobe noted that the optical system is not required to have configurationas shown in FIG. 8A and FIG. 8B, but if there is employed such aconfiguration capable of preparing holographic stereogram, e.g.,incident direction of reference light, the number of lenses, the kindthereof and combination thereof may be suitably changed.

[0093] As shown in FIG. 8A, the exposure processing unit 23 comprises alaser light source 31 for emitting laser beams of a predeterminedwavelength, and a shutter 32 for exposure and a half mirror 33 disposedon the optical axis of laser beams L1 from the laser light source 31.

[0094] The exposure shutter 32 is closed when the recording medium 1 forhologram is not exposed and is opened when the recording medium 1 forhologram is exposed. In addition, the half mirror 33 serves to separatelaser beams L2 passed through the exposure shutter 32 into referencelight and object light. Light L4 reflected by the half mirror 33 servesas reference light and light L3 transmitted through the half mirror 33serves as object light.

[0095] On the optical axis of light L4 reflected by the half mirror 33,as the optical system for reference light, there are arranged acylindrical lens 40, a collimator lens 41 for changing reference lightinto parallel light, a total reflection mirror 42 for reflecting lightconfigured to be parallel light by the collimator lens 41 in orderrecited.

[0096] The light reflected by the half mirror 33 is then firstconfigured to be divergent light by the cylindrical lens 40 and is thenconfigured to be parallel light by the collimator lens 41. Thereafter,such parallel light is reflected by the total reflection mirror 42 andis incident on the recording medium 1 for hologram.

[0097] On the other hand, on the optical axis of light L3 transmittedthrough the half mirror 33, as shown in FIGS. 8A and 8B, as the opticalsystem for object light, there are disposed a total reflection mirror 34for reflecting transmitted light from the half mirror 33, a spatialfilter 35 in which convex lens and pin hole are combined, a collimatorlens 36 for allowing object light to be in parallel, a display section37 for displaying picture image to be recorded, and a cylindrical lens38 for converging object light onto the recording medium 1 for hologramin order recited.

[0098] Thus, light L3 transmitted through the half mirror 33 isreflected by the total reflection mirror 34, and is then allowed to bediffused-light from spot light source by the special filter 35. Then,such diffused light is configured to be parallel light by the collimatorlens 36 and is then incident on the display section 37. In this example,the display section 37 is e.g., a picture display section of thetransmission type comprised of liquid crystal panel, and serves todisplay picture image based on picture data. D4 sent from the controlcomputer 22. Furthermore, light transmitted through the display section37 is modulated in accordance with picture image displayed on thedisplay section-37, and is then incident on the cylindrical lens 39.

[0099] In addition, light transmitted through the display section 37 isconverged in lateral direction by the cylindrical lens 39, and thisconvergent light is incident on the recording medium 1 for hologram asobject light. Namely, in this exposure processing unit 23, projectedlight from the display section 37 is incident upon the recording medium1 for hologram as strip-shaped rays of object light.

[0100] In this case, with respect to reference light and object light,reference light is configured to be incident on one principal surface ofthe recording medium 1 for hologram and object light is configured to beincident on the other principal surface of the recording medium 1 forhologram. Namely, reference light is configured to be incident at apredetermined incident angle on one principal surface of the recordingmedium 1 for hologram, and object light is configured to be incident onthe other principal surface of the recording medium 1 for hologram insuch a manner that the optical axis is substantially perpendicular tothe recording medium 1 for hologram. Thus, the reference light and theobject light interfere with each other on the recording medium 1 forhologram. As a result, interference patterns taking place by suchinterference are recorded onto the recording medium 1 for hologram aschanges of refractive index.

[0101] Moreover, this exposure processing-unit 23 comprises printer-headportion 43 which can intermittently feed the recording medium 1 forhologram under control of the control computer 22. This exposureprocessing unit 23 carries out intermittent feed of the recording medium1 for hologram by one element hologram on the basis of control signalfrom the control computer 22 every time one picture image is recorded asone element hologram with respect to the recording medium 1 for hologramwhich has been set in a predetermined state at the printer head portion43. Thus, picture images based on picture data processed at the dataprocessing unit 21 are recorded in succession onto the recording medium1 for hologram as element hologram in a manner such that they aresuccessive in the lateral direction.

[0102] This exposure processing unit 23 displays, on the display section37, picture image for exposure based on picture data. Furthermore, theshutter 32 for exposure is opened by a predetermined time so that therecording medium 1 for hologram is exposed.

[0103] At this time, light L4 which has been reflected by half mirror 33of laser beams L2 emitted from laser light source 31 and transmittedthrough the shutter 32 for exposure is incident on the recording medium1 for hologram as reference light. In addition, light L3 which has beentransmitted through the half mirror 33 results in projected light inwhich picture image displayed on the display section 37 is projected,and such projected light is incident on the recording medium 1 forhologram as object light. Thus, picture image for exposure displayed onthe display section 37 is recorded as strip-shaped element picture ontothe recording medium 1 for hologram.

[0104] Furthermore, when recording of one picture image onto therecording medium 1 for hologram is completed, the recording medium 1 forhologram is then fed by one element hologram by the printer head portion43.

[0105] The above-mentioned operations are repeated in the state wherepicture images for exposure configured to be displayed on the displaysection 37 are changed in succession in order of parallax picture train.Thus, picture images for exposure based on the original picture data arerecorded in succession as strip-shaped element picture onto therecording medium 1 for hologram.

[0106] The printer head portion 43 will be described in detail withreference to FIG. 9. This printer head portion 43 is adapted so thatthere are disposed in succession a film cartridge 71, rollers 70, 72 forintermittent feeding, an optical part 76, a pinch roller 73, anultraviolet lamp 77, a heat roller 78, a pair of feed rollers 79A, 79Bfor feed ejection, and a cutter 80.

[0107] This printer head portion 43 is adapted to rotatably axiallysupport, with a predetermined torque, intermittent feeding roller, 70within the film cartridge 71 loaded at a predetermined position, and canhold the recording medium 1 for hologram drawn out from the filmcartridge 71 in such a manner that it is put between the intermittentfeeding rollers 70, 72 and the pinch roller 73. Thus, the recordingmedium 1 for hologram is held in a manner substantially perpendicular tothe object light between the intermittent feeding roller 70 and theintermittent feeding roller 72.

[0108] The intermittent feeding roller 70 and the intermittent feedingroller 72 are biassed in directions away from each other by torsion coilspring (not shown). Thus, a predetermined tension is applied to therecording medium 1 for hologram disposed in such a manner to bridgeacross the intermittent feeding roller 70 and the intermittent feedingroller 72. As a result, position of the recording medium 1 for hologramis stabilized and vibration is suppressed. It is to be noted that such atension may be applied by the pinch roller system or sprocket feedsystem, etc.

[0109] The optical part 76 is adapted so that one-dimensional diffusionplate 74 and a louver film 75 are integrally stuck in the state wherethey are curved, and is disposed coincided with incident position ofobject light between the intermittent feeding roller 70 and theintermittent feeding roller 72. This optical part is movably held in adirection close to the recording film 1 for hologram or away therefromas indicated by arrow b by optical part drive mechanism (not shown).

[0110] In this example, the one-dimensional diffusion plate 74 serves toallow holographic stereogram to have angle of visibility in thelongitudinal direction. Namely, by this one-dimensional diffusion plate74, object light is diffused in the longitudinal direction, i.e., in thelong axis direction of element hologram to be made or prepared. Thus,holographic stereogram to be made or prepared has angle of visibility inthe longitudinal direction.

[0111] In addition, the louver film 75 is an optical part having finereed screen-shaped lattice, and serves to'prevent that reference lighttransmitted through the recording medium 1 for hologram is reflected bythe one-dimensional diffusion plate 74 and is incident on the recordingmedium 1 for hologram for a second time.

[0112] The printer head portion 43 is driven on the basis of controlsignal delivered from the control computer 22 before exposure operationis started to move the optical part 76 in a direction close to therecording medium 1 for hologram. Thus, the optical part 76 is pressedonto the recording medium 1 for hologram loaded between the intermittentfeeding roller 70 and the intermittent feeding roller 72. By pressingthe optical part 76 onto the recording medium 1 for hologram in thisway, it is possible to suppress very small vibration of the recordingmedium 1 for hologram. By suppressing very small vibration of therecording medium 1 for hologram as stated above, it becomes possible tomake (prepare) holographic stereogram excellent in the diffractionefficiency and in which bright reproduction image can be obtained.

[0113] The intermittent feeding rollers 70, 72 are adapted so that theycan be desirably rotated in the direction as indicated by arrow c bystepping motor (not shown). This stepping motor rotates intermittentfeeding rollers 70, 72 every completion of exposure corresponding to onepicture image on the basis of control-signal S2 delivered from thecontrol computer 22 so that the recording medium 1 for hologram is sentby one element hologram every completion of exposure corresponding toone picture image.

[0114] The ultraviolet lamp 77 serves to irradiate ultraviolet rays Lbto the recording medium 1 for hologram sent by the intermittent feedingroller 72. As the result of the fact that ultraviolet rays areirradiated onto the recording medium 1 for hologram by this ultravioletlamp 77, polymerization of monomer M of the hologram recording layer 3of the recording medium 1 for hologram is completed.

[0115] The heat roller 78 is provided with heating means such as heater,etc. therewithin, and is adapted so that the peripheral surface of theheat roller 78 can maintain temperature of about 120° C. Furthermore,this heat roller heats the recording medium 1 for hologram to therebyincrease refractive index modulation degree of the hologram recordinglayer 3 to fix recording picture image of the hologram recording layer3.

[0116] Ejecting feeding rollers 79A, 79B at the succeeding stage of theheat roller 78 are rotated in a manner synchronous with intermittentfeeding roller 72 by drive mechanism (not shown) supplied with controlsignal from the control computer 22. Thus, the protective layer 4 can besecurely held in the state tightly in contact with the peripheral sidesurface of the heat roller 78 without allowing the recording medium 1for hologram to be loosened between the intermittent feeding roller 72and the ejecting feeding rollers 79A, 79B.

[0117] Moreover, drive mechanism (not shown) for the cutter 80 drivesthe cutter 80 at the stage where all area portions in which pictureimage of the recording medium 1 for hologram 1 is recorded are ejectedtoward the external with respect to the cutter 80 after respectivepicture images based on respective picture data of parallax picturetrain are recorded onto the recording medium 1 for hologram on the basisof control signal delivered from the control computer 22 to therebyseparate such portions from other portions. Thus, portions whererespective picture data of parallax picture train are recorded of therecording medium 1 for hologram can be ejected toward the external asone holographic stereogram.

[0118] In recording three-dimensional picture image onto the recordingmedium 1 for hologram by the printer head portion 43 as described above,control signal is first sent out from the control computer 22 to theoptical part drive mechanism of the printer head portion 43 in the statewhere the recording medium 1 for hologram is loaded across theintermittent feeding roller 70 and the intermittent feeding roller 72 todrive the optical part drive mechanism to press the optical part 76 ontothe recording medium 1 for hologram at a predetermined pressure.

[0119] Then, picture data D4 is sent out from the control computer 22 tothe display section 37 of the exposure processing unit 23 to allow thedisplay section 37 to display picture image for exposure based on thispicture data D4, and to send out control signal S1 from the controlcomputer 22 to the shutter 32 to open the shutter 32 by a predeterminedtime to expose the recording medium 1 for hologram.

[0120] At this time, light L4 which has been reflected by half mirror 33of laser beams emitted from the laser light source 31 and transmittedthrough the shutter 32 is incident on the recording medium 1 forhologram as reference light. Furthermore, light L3 which has beentransmitted through the half mirror 33 results in projected light inwhich picture image displayed on the display section 37 is projected,and this projected light is incident on the recording medium 1 forhologram as object light. In this way, picture image for exposureconfigured to be displayed on the display section 37 is recorded ontothe recording medium 1 for hologram as rectangular element hologram.

[0121] Furthermore, after recording of one picture image onto therecording medium for hologram is completed, control signal S2 is thensent out from the control computer 22 to the printer head portion 43 tofeed the recording medium 1 for hologram by one element hologram.

[0122] The above-mentioned operations are repeated in the state wherepicture images for exposure configured to be displayed on the displaysection 37 are changed in succession in order of parallax picture train.Thus, picture images for exposure based on picture data processed by thedata processing unit 21 are recorded in succession onto the recordingmedium 1 for hologram as rectangular element hologram.

[0123] As described above, in this holographic stereogram preparingapparatus, plural picture images for exposure based on output of thedata processing unit 21 are displayed in succession on the displaysection 37 and shutter 32 is opened every respective picture images.Thus, respective picture images are respectively recorded in successiononto the recording medium 1 for hologram as rectangular elementholograms. At this time, since the recording medium 1 for hologram isfed by one element hologram every one picture image, respective elementholograms are recorded onto the recording medium 1 for hologram asplural element holograms successive in lateral direction. Thus,holographic stereogram having parallax in the lateral direction can beobtained.

[0124] Thereafter, ultraviolet rays are irradiated over the entiresurface of the recording medium 1 for hologram thus exposed byultraviolet lamp 77 at the printer head portion 43. Thus, polymerizationof monomer M at the hologram recording layer 3 of the recording medium 1for hologram is completed. Furthermore, at the succeeding stage of thisultraviolet lamp 77, the recording medium 1 for hologram is heated byheat roller 78. As a result, refractive index modulation degree of thehologram recording layer 3 is increased, thereby the recording pictureimage being fixed.

[0125] Here, there will be added explanation relating to refractiveindexes of base and protective layer of the recording medium forhologram in the case where the optical system shown in FIG. 8, i.e., theoptical system for allowing reference light to be obliquely incident,which is so called off-axis hologram optical system is used.

[0126] In the above-described second model, there has been given, forsimplification of the model, explanation with respect to the opticalsystem where reference light is incident in a manner perpendicular tothe recording medium for hologram, which is so called on-axis hologramoptical system.:

[0127] Due to-the difference between the off-axis hologram opticalsystem and the on-axis hologram optical system, consideration must betaken in connection with

[0128] (1) “refraction of rays of light by difference of refractiveindex when reference light is incident from air to base, and change ofdirection of rays of light based thereon”,

[0129] (2) “Change of transmission distance by thickness of the basebased on the fact that rays of light are perpendicularly transmittedwithin the base into transmission distance of actual rays of light basedon the fact that rays of light are obliquely transmitted within thebase”,

[0130] (3) “Refractive index vector within the base changes independency upon direction where rays of light are incident on the baseby the geometrical relationship between axis of double refraction ofbase and direction in which rays of light are incident on the base”, andthe like.

[0131] However, also in all of the above-mentioned (1), (2), (3), byreplacing physical quantity such as propagation direction of rays oflight by difference of optical system, etc. or limiting materialproperty of optical material, the previously described model can beapplied.

[0132] With respect to the item (1), direction of rays of light afterthey are incident is first determined by the Snell laws (rule ofreflection/refraction) from the state of double refraction whenreference light is incident on the base. Furthermore, since the,direction of rays of light is direction of rays of light transmittedthrough the base, the state of double refraction with respect to thatdirection is replaced by the state of double refraction in thepreviously described model so that the previously described model can beapplied.

[0133] With respect to the item (2), since phase change based on thefact that rays of light are passed through the base is determined inaccordance with transmission distance of actual rays of light based onthe-fact that rays of light are obliquely transmitted through the base,it is sufficient to replace thickness d^(ref) of the base by actualtransmission distance of rays of light.

[0134] With respect to the item (3), as the optical state of the examplewhere uniaxial optical material is used is illustrated by usingrefractive index elliptical body in the above-mentioned drawing,refractive index vector of base changes in dependency upon whether raysof light are perpendicularly incident or are obliquely incident. Byusing the explanation of the item (1) while paying attention to therelationship between incident angle and refractive index vector toreplace the state of double refraction with respect to direction of raysof light by the state of double refraction in the previously describedmodel, it is possible to apply the previously described model.

[0135] The relationship between the incident angle and the refractiveindex vector will be described in a comparative manner with reference tothe above-mentioned FIGS. 6A, 6B, 6C and FIG. 10.

[0136] In FIG. 6A, axial direction Y of double refraction of uniaxialoptical material is configured to be thickness direction of strip-shapedrecording medium 65 for hologram. By doing so, there results the statewhere there is no double refraction with respect to laser beams Lperpendicularly incident on the recording medium 65 for hologram.However, there results the state where there is double refraction withrespect to laser beams L obliquely incident on the recording medium 65for hologram. Accordingly, it is necessary to apply the relationshipbetween direction of linear polarization and direction of the axis alongthe model of the previously described on-axis hologram optical system.

[0137] In FIG. 6B, axial direction Y of double refraction of uniaxialoptical material is configured to be a direction of the longer side ofrecording medium 66 for hologram. By doing so, it is easy that directionof linear polarization is configured to be the same state as that of theaxial direction of double refraction, or perpendicular state theretowith respect to laser beams L incident on the recording medium 66 forhologram. Here, FIG. 10A shows the state of double refraction in thecase where incident plane of incident laser beams is in parallel to thedirection of the longer side, and FIG. 10B shows the state of doublerefraction in the case where incident plane of incident laser beams isperpendicular to the direction of the longer side. In FIG. 10A, doublerefraction n′ in the case where laser beams L′ are incident at incidentangle θ′ which is perpendicular to the recording medium for hologram anddouble refraction n″ in the case where laser beams L″ are incident atincident angle θ″ which is oblique with respect to the recording mediumfor hologram are different from each other. On the other hand, in FIG.10B, both double refractions are the same.

[0138] In FIG. 6C, axial direction Y of double refraction of uniaxialoptical material is configured to be coincided with a direction of theshorter side of the strip-shaped recording medium 67 for hologram.Thereby, it is easy that direction of linear polarization is configuredto be the same as axial direction of double refraction or perpendicularthereto with respect to laser beams L incident on the recording medium67 for hologram. Here, FIG. 10A shows the state of double refraction inthe case where incident plane of incident laser beams is in parallel toa direction of the shorter side, and FIG. 10B shows the state of doublerefraction in the case where incident plane of incident laser beams isperpendicular to a direction of the shorter side. In FIG. 10A, doublerefraction n′ in the case where laser beams L′ are incident at incidentangle θ′ which is perpendicular to the recording medium for hologram anddouble refraction n″ in the case where laser beams L″ are incident atincident angle 0″ which is oblique with respect to the recording mediumfor hologram are different from each other. On the other hand, in FIG.10B; both double refractions are the same.

[0139] From the above result, such an approach is employed to useuniaxial optical material as optical material constituting the recordingmedium for hologram with respect to geometrical shape of strip-shapedrecording medium for hologram having the longer side-and the shorterside, etc., and to allow axial direction of that double refraction to becoincided with the longer side or the shorter side, thereby making itpossible to univocally determine polarization state of the hologramrecording unit also in the off-axis hologram optical system where laserbeams are obliquely incident on the recording medium for hologram.Accordingly, unification and standardization can be made in bothhologram recording unit and recording medium for hologram. Thus, massproduction can be carried out and reduction in cost can be realized.

[0140] While the example where reference light is passed/emitted throughthe base and is incident on the hologram recording layer, and objectlight is passed/emitted through the protective layer and is incident onthe hologram recording layer has been explained, it is needless to saythat there may be made change into the example where reference light andobject light are exchanged, and object light is passed/emitted throughthe base and is incident on the hologram layer, and reference light ispassed/emitted through the protective layer and is incident on thehologram recording layer.

[0141] In addition, while explanation has been given in connection withthe recording medium for hologram consisting of three layers of thebase, the hologram recording layer and the protective layer, there maybe employed recording media for hologram consisting of five and sevenlayers of base, hologram recording layer, intermediate layer andprotective layer, etc. as shown in FIGS. 11 and 12, respectively. Alsoin this case, it is desirable that the relationship of doublerefraction, polarization and geometrical shape of the intermediate layeris configured to be the same as the relationship of double refraction,polarization and-geometrical shape of the above-described base andprotective layer.

[0142] Explanation will be given in connection with other two morepractical examples of recording media for-hologram with reference toFIGS. 11 and 12. First, recording medium 5 for hologram shown in FIG. 11is a recording medium of five layers obtained by forming a firsthologram recording layer 7 consisting of photo-polymer layer on a base 6to form a second hologram recording layer 9 through an intermediatelayer 8 consisting of colorless and transparent resin film layer thereonto further form a protective layer 10 thereon.

[0143] Also in this recording medium 5 for hologram, it is similarlydesirable to employ material called non-double refraction opticalpolymer as described above as the base 6, the intermediate layer 8 andthe protective layer 10. Furthermore, axial direction of doublerefraction of materials of the base 6, the intermediate layer 8 and theprotective layer 10 is configured to be coincided with the geometricalshape of the photo-polymer film used as the hologram recording layers ina manner as stated above.

[0144] In addition, axial direction of double refraction of materials ofthe base 6, the intermediate layer 8 and the protective layer 10 isconfigured to be coincided with polarization of reference light andobject light at the exposure processing unit of the holographicstereogram preparing apparatus.

[0145] Thus, also in this recording medium 5 for hologram, it ispossible to generate bright and uniform holographic stereogram withoutlowering contrast of interference patterns formed at the hologramrecording layer comprised of photo-polymer layer.

[0146] Furthermore, a recording medium 11 for hologram shown in FIG. 12is a recording medium of seven layers obtained by forming a firsthologram recording layer 13 comprised of photo-polymer layer on a base12 to form a second hologram recording layer 15 through an intermediatelayer 14 comprised of colorless and transparent resin film layer thereonto further form thereon a third hologram recording layer 17 through anintermediate layer 16 thereafter to form a protective layer 18 thereon.

[0147] Also in this recording medium 11 for hologram, it is desirable toemploy material called non-double refraction optical polymer asdescribed above as the base 12, the intermediate layers 14 and 16, andthe protective layer 18.

[0148] Furthermore, axial direction of double refraction of materials ofthe base 12, the intermediate layers 14 and 16, and the protective layer18 is configured to be coincided with the geometrical shape of thephoto-polymer film used as the hologram recording layers 13, 15 and 17as described above.

[0149] Furthermore, axial direction of double refraction of materials ofthe base 12, the intermediate layers 14 and 16, and the protective layer18 is configured to be coincided with polarization of reference lightand object light at the exposure processing unit of the holographicstereogram preparing apparatus in a manner as described above.

[0150] Also in this recording medium 11 for hologram, it is thereforepossible to generate bright and uniform holographic stereogram withoutlowering contrast of interference patterns formed at the hologramrecording layer comprised of photo-polymer layer.

[0151] It is to be noted that the hologram recording layers of themulti-layer structure shown in FIGS. 11 and 12 have excellentcharacteristic with respect to wavelength of three primary colors of R,G, B and are used for generating color holographic stereogram.

[0152] Furthermore, while the recording medium for hologram composed ofbase, hologram recording layer, intermediate layer and protective layerhas been described above, there may be provided adhesive layers betweenrespective layers for the purpose of bonding or adhering respectivelayers. At this time, from an optical point of view in the presentinvention, it can be considered that adhesive layers put betweenrespective layers contribute to double refraction in one body as aportion of the base, the intermediate layer or the protective layerrespectively adjacent. Namely, the above-mentioned model can be appliedas layer which provides phase change in one body.

[0153] In addition, while explanation has been given by usingphoto-polymer as photosensitive material of the hologram recordinglayer, the present invention is not limited to such material. There maybe used other photosensitive material such as silver salt material orgelatin dichromate, etc.

INDUSTRIAL APPLICABILITY

[0154] By using the present invention as described above, it is possibleto record bright and uniform hologram without lowering contrast ofinterference patterns formed at the hologram recording layer comprisedof photo-polymer layers.

1. (Amended) A recording medium for hologram comprising a hologramrecording layer in which object light indicating a picture image to berecorded and reference light are irradiated so that hologram isrecorded, and a base and a protective layer to put the hologramrecording layer in between, wherein the recording medium for hologramhas rectangular shape, and the base and the protective layer comprisematerial through which light is transmitted and in which an axialdirection of double refraction is parallel or nearly parallel to eitherone side of the rectangular shape.
 2. (Amended) The recording medium forhologram as set forth in claim 1, wherein the material configuring thebase and the protective layer is material in which optically transparentpolymer material is configured to be in film form, and the polymermaterial configured to be in film form is fabricated into a tape shapethat is elongated in one direction side, and the axis of doublerefraction of the film is coincided with a direction of the longer sideof the tape shape or is perpendicular thereto.
 3. (Amended) Therecording medium for hologram as set forth in claim 1, furthercomprising one layer or more in addition to the hologram recordinglayer, the base and the protective layer.
 4. (Amended) The recordingmedium for hologram as set forth in claim 1, wherein plural elementholograms constituting holographic stereogram are recorded on thehologram recording layer.
 5. (Amended) A hologram producing apparatuscomprising a supply unit for a recording medium for hologram, and anexposure unit for irradiating object light and reference light onto arecording medium for hologram supplied from the supply unit to recordhologram, wherein the recording medium for hologram comprises a hologramrecording layer on which hologram is recorded, and a base and aprotective layer between which the hologram recording layer is put, andthe recording medium for hologram is formed in rectangular shape, thebase and the protective layer comprise material through which light istransmitted and in which an axial direction of that double refraction isparallel or nearly parallel to either one side of the rectangular shape,and the object light and the reference light that the exposure unitirradiates are linearly polarized light polarized in a direction equalor nearly equal to the axial direction of double refraction.
 6. (Added)A method of preparing a recording medium for hologram comprising ahologram recording layer in which object light indicating a pictureimage to be recorded and reference light are irradiated so that hologramis recorded, and other layer laminated on the hologram recording layer,wherein a shape of the recording medium for hologram is configured to berectangular, and the other layer comprises material through which lightis transmitted, and in which an axial direction of double refraction isparallel or nearly parallel to either one side of the rectangular shape.7. (Added) A hologram producing method of supplying a recording mediumfor hologram from a supply unit to irradiate object light and referencelight onto the recording medium for hologram to thereby producehologram, wherein the recording medium for hologram comprises a hologramrecording layer on which hologram is recorded, and other layer laminatedon the hologram recording layer, and is formed into a rectangular shape,the other layer comprises material through which light is irradiated andin which an axial direction of double refraction is parallel or nearlyparallel to either one side of the rectangular shape, and linearlypolarized light polarized in a direction equal or nearly equal to theaxial direction of double refraction is used as the object light and thereference light.